Various heat transfer recording methods have been known so far. Among these methods, dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver halide photography (see, for example, “Joho Kiroku (Hard Copy) to Sono Zairyo no Shintenkai (Information Recording (Hard Copy) and New Development of Recording Materials)” published by Toray Research Center Inc., 1993, pp. 241-285; and “Printer Zairyo no Kaihatsu (Development of Printer Materials)” published by CMC Publishing Co., Ltd., 1995, p. 180). Moreover, this system has advantages over silver halide photography: it is a dry system, it enables direct visualization from digital data, it makes reproduction simple, and the like.
In this dye diffusion transfer recording system, a heat-sensitive transfer sheet (hereinafter also referred to as an ink sheet) containing dyes is superposed on a heat-sensitive transfer image-receiving sheet (hereinafter also referred to as an image-receiving sheet), and then the ink sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the ink sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta, and yellow, or four colors which consists of the three colors and black, are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
In such the recording system, the heat-sensitive transfer sheet and the heat-sensitive transfer image-receiving sheet are heated at the state of superposition. Consequently, releasing properties between them after transfer are important. In the case where the releasing properties are insufficient, there was a problem that the sticking occurred, resulting in unevenness of print density.
There are proposed a method of depositing a silicone graft polymer and a polysiloxane compound on the heat-sensitive transfer sheet (JP-A-9-202058 (“JP-A” means unexamined published Japanese patent application)) and a method of depositing a releasing agent comprising a copolymer of silicone and a polyamidoimide resin on the heat-sensitive transfer sheet (JP-A-2003-159880). However, from recent demands for speeding-up of printing, further improvement has been desired.